Many of the actions of growth factors on cells are thought to be mediated by a family of inositol phosphoglycan (IPG) second messengers[13]. It is thought that the source of IPGs is a “free” form of glycosyl phosphatidylinositol (GPI) situated in cell membranes. IPGs are thought to be released by the action of phosphatidylinositol-specific phospholipases following binding of growth factors to receptors on the cell surface. There is evidence that IPGs mediate the action of a large number of growth factors including insulin, nerve growth factor, hepatocyte growth factor, insulin-like growth factor I (IGF-I), fibroblast growth factor, transforming growth factor β, the action of IL-2 on B-cells and T-cells, ACTH signalling of adrenocortical cells, IgE, FSH and hCG stimulation of granulosa cells, thyrotropin stimulation of thyroid cells, cell proliferation in the early developing ear and rat mammary gland.
Partially characterised inositolphosphoglycans (IPGs) have been postulated to mediate the action of a number of growth factors including insulin and insulin-like growth factor I (IGF-I)[1]. Despite their isolation from several tissues type, the precise chemical structures of these IPGs are, however, still unknown and two main structural groups have been proposed on the basis of the chemical composition[2,3] which display different biological activity and tissue distribution[4]; the family of glucosamine-myo-inositol containing IPGs (IPG-A) and the family of chiro-inositol-galactosamine containing IPGs (IPG-P).
In an attempt to establish the minimal structural requirements for biological activity, a number of compounds containing some of the basic structural motifs that have been postulated for IPG mediators have been synthesised in the art[5]. These synthetic compounds include O-(2-amino-2-deoxy-D-glucopyranosyl)-α(1-6)-chiro-inositol 1-phosphate and O-(2-amino-2-deoxy-D-glucopyranosyl)-α(1-6)-myo-inositol 1-phosphate[6].
U.S. Pat. No. 6,004,938 (Hoechst) discloses a group of synthetic inositol glycans having insulin-like action. The compounds are based on 2-6 monsaccharide units linked to an inositol moiety. The examples in the patent all employ myo-inositol and are composed of 5 or 6 units apart from two pseudo-trisaccharide compounds G and H. Compounds G and H are HO—PO(H)O-6Man-α(1-4)-GluN-α(1-6)-(L)inositol-1,2(cyclic) phosphate and HO—PO(H)O-6Man-α(1-4)-GluN-α(1-6)-(L)inositol, otherwise known as O-(6-hydrogenphosphonate-α-D-mannopyranosyl)-(1-4)-(2-ammonio-2-deoxy-α-D-glucopyranosyl)-(1-6)-L-myo-inositol-1,2-cyclic phosphate and O-(6-hydrogenphosphonate-α-D-mannopyranosyl)-(1-4)-(2-amino-2-deoxy-α-D-glucopyranosyl)-L-myo-inositol. The properties of exemplified compounds are investigated in lipogenesis and glucose transport assays employing rat fat cells.
WO96/14075 (University of Virginia) discloses a generic family of compounds D-hexosamines linked to an inositol via a β1,4-linkage. The inositols can be myo or chiro-inositol or pinitol, while the hexosamines are glucosamine or galactosamine. However, this application describes the synthesis of just two compounds 4-O-(2-deoxy-2-amino-β-D-galactopyranosyl)-D-pinitol and 4-O-(2-deoxy-2-amino-β-D-galactopyranosyl)-D-chiro-inositol, or in IUPAC notation O-(2-amino-2-deoxy-β-D-galactopyranosyl)-(1-4)-D-pinitol and O-(2-amino-2-deoxy-β-D-galactopyranosyl)-(1-4)-D-chiro-inositol.
WO99/06421 (University of Virginia) describes synthetic insulin mimetic substances and includes a general formula I showing β1,4-linked disaccharides. However, despite this the compounds synthesised in this application are exactly the same as those disclosed in the applicant's earlier application, WO96/14075.
A multi-step synthesis of a IPG-P mimetic from glucose has been previously reported in Jaramillo et al[6], which discloses a compound called C4, 1-D-6-O-(2-amino-2-deoxy-α-D-glucopyranosyl)-chiro-inositol 1-phosphate. A further synthesis of C4 is described in our co-pending International Patent Application PCT/GB99/03715 (Rademacher Group Limited). Zapata et al[16 ] discloses three other compounds C1-C3 which are:    C1 1-D-4-O-(2-amino-2-deoxy-α-D-glucopyranosyl)-myo-inositol 1-phosphate.    C2 1-D-6-O-(2-amino-2-deoxy-α-D-glucopyranosyl)-myo-inositol 1-phosphate.    C3 1-D-6-O-(2-amino-2-deoxy-α-D-glucopyranosyl)-myo-inositol 1,2 cyclic-phosphate.    C4 1-D-6-O-(2-amino-2-deoxy-α-D-glucopyranosyl)-chiro-inositol 1-phosphate.
It remains a significant problem in the art to produce synthetic compounds which can mimic one or more of the activities of inositol phosphoglycans or which act as antagonists of IPGs.